If you add a method, keep in mind two things: (1) the first argument will
always be a list of nodes from which to filter. In the case of context
methods (such as position), the function should return an array with a
value for each child in the array. (2) all method calls from XML will have "-" replaced with
"_". Therefore, in XML,
"local-name()" is identical (and actually becomes)
"local_name()"